linux-kernel - Re: [PATCH 3.19 091/123] gadgetfs: use-after-free in ->aio

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Date:	Wed, 25 Mar 2015 10:23:27 +0100
From:	Alexander Holler <holler@...oftware.de>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 3.19 091/123] gadgetfs: use-after-free in ->aio_read()

Am 25.03.2015 um 09:33 schrieb Greg Kroah-Hartman:
> On Tue, Mar 24, 2015 at 07:06:56PM +0100, Alexander Holler wrote:
>> Am 24.03.2015 um 18:58 schrieb Greg Kroah-Hartman:
>>> On Tue, Mar 24, 2015 at 06:30:17PM +0100, Alexander Holler wrote:
>>>> Am 24.03.2015 um 16:46 schrieb Greg Kroah-Hartman:
>>>>> 3.19-stable review patch.  If anyone has any objections, please let me know.
>>>>>
>>>>> ------------------
>>>>>
>>>>> From: Al Viro <viro@...iv.linux.org.uk>
>>>>>
>>>>> commit f01d35a15fa04162a58b95970fc01fa70ec9dacd upstream.
>>>>
>>>> Just what I've thought. Please see
>>>>
>>>> https://lkml.org/lkml/2015/3/15/5
>>>
>>> I have no idea what you are asking me to do here, please be specific.
>>
>> In order to not become blamed for mangling some language, here's a machine
>> generated output:
>>
>> ------
>> wandq linux # git co -b t v3.19.2
>> Switched to a new branch 't'
>> wandq linux # git am /tmp/\[PATCH\ 3.19\ 091_123\]\ gadgetfs\:\
>> use-after-free\ in\ -\>aio_read\(\).eml
>> Applying: gadgetfs: use-after-free in ->aio_read()
>> wandq linux # make drivers/usb/gadget/legacy/gadgetfs.ko
>> (...)
>>    CALL    scripts/checksyscalls.sh
>>    CC [M]  drivers/usb/gadget/legacy/inode.o
>> drivers/usb/gadget/legacy/inode.c: In function 'ep_aio_rwtail':
>> drivers/usb/gadget/legacy/inode.c:642:12: warning: 'value' may be used
>> uninitialized in this function [-Wmaybe-uninitialized]
>>    ssize_t   value;
>>              ^
>>    LD [M]  drivers/usb/gadget/legacy/gadgetfs.o
>> (...)
>> ------
>
> Is there a specific patch that is in Linus's tree that fixes this issue
> that I should be applying to the stable tree?

No specific one. The changes of this patch were discarded by other 
patches in Linus tree which fixed other problems of gadgetfs too.

Besides that the solution for this one specific patch is a one-liner, 
I'll give a short overview:

- gadgetfs is already unusable since 3.16 (even with this patch) because 
(p)read/(p)write doesn't work (fixed with 4.0)
- the problem this patch fixes is unlikely to be hit because glibc 
doesn't use the Linux aio-syscall, but pread/pwrite, which means someone 
has to use a special lib and not aio(7) to end up at the syscall the 
patch in question fixes.
- there aren't that many users of gadgetfs

No idea if you want to apply or backport the whole series found in Al 
Viros vfs.git/gadgetfs.

Regards,

Alexander Holler
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